The present invention relates to surface mount type electrical connectors to be mounted on a printed circuit board (PCB) in such a manner that the contacting sections of contactors in an insulating housing may be superposed on the conductors of the PCB for making connection.
Recently, various types of compact electronic equipment have been assembled by machines. As a result, there has been a need for high density and automatic mounting of various electronic components on a PCB. In response to such a need, Japanese Patent Kokai No. 60-140688 has proposed a surface mount type electrical connector. This surface mount type electrical connector is mounted on a PCB in such a manner that the legs (connecting sections) of contacts may be soldered to the electrical circuits (conductive pads).
FIG. 10 shows such a conventional surface mount type electrical connector 3 which is mounted on a PCB 2, with the legs 8 of its contacts 5A-5C soldered on conductive pads 2A by reflow soldering technique. By the reflow soldering technique, after the conductive pads 2A have been formed or cream solder has been applied to the circuit, the legs 8 are soldered by heating either the entire PCB-connector assembly in a furnace or only the legs with laser or infrared rays to melt the solder for making connection. Because of a difference in thermal expansion coefficient between the connector housing and the PCB, there are produced stresses between the legs and the pads after cooling. These stresses are absorbed by spring arms 7 to certain degrees. The housing 4 also has a pair of depending studs 9.
However, the above conventional surface mount type electrical connector has the following disadvantages.
(1) The tail portions 6 of contacts extending from an end of the housing 4 are not protected so that they can cause short-circuit or deformation when a foreign object contacts or strikes them. In addition, the tail portion 6 can be easily bent during soldering so that the leg is offset from the conductive pad, making soldering connection impossible.
(2) When several contacts are arranged in one layer upon another in the housing, the length of the top contact arm 7 is longer than those of lower contact arms 7. Consequently, the degrees to which they can absorb the stresses produced upon soldering are different. More specifically, if the bottom contact arm 7 is shortened for compactness, it would not fully absorb the stress, whereas if it is lengthened to assure absorption of the stress, the connector becomes larger, preventing its high density mounting on a PCB.
(3) The depending studs 9 of the housing 4 are inserted into mounting apertures of a PCB but not firmly secured to the PCB. Consequently, as the connector-PCB assembly is transported for soldering, the connector can be separated from the PCB due to vibrations or impacts. Even after soldering, the soldered portions can be separated by external forces. In addition, the housing can bend backward and come off from the PCB because of their different thermal expansion coefficients upon cooling, making the soldered portions separate.